After having a long deep think I finally decided to release the design files for all my published works. Since I’ve always been taught to protect my copyrights and source files it was a big step, but I’m confident it’s the right way to go.
You can read a bit more about it on blendernation and my post at the blenderartists forum.
I chose to release under the Creative Commons Attribution 3.0 license. This means that anyone can use my works for anything they want, as long as they mention me as the creator/source of the design.